An optical system of the projection-type display apparatus using a reflection-type light valve is classified broadly into two types: a telecentric type and a non-telecentric type. The telecentric optical system uses a prism so that a projection lens is telecentric with respect to a reflection-type light valve. The non-telecentric type optical system does not use a prism, and is so configured that the projection lens is not telecentric with respect to the reflection-type light valve.
Recently, there is proposed a projection-type display apparatus having a function to shift a projection lens in a vertical direction or the like (i.e., a lens shift function), so as to arbitrarily move a projection area without moving a main body of the apparatus. In order to accomplish such a lens shift function, it is proposed to employ a telecentric optical system using a total reflection prism (for example, see Patent Document 1).
In contrast, there is proposed an optical system using a condenser lens that introduces the light from a light source to the DMD and a projection lens that projects the light reflected by the DMD, and is configured to change the angle of incidence on the DMD by decentering the condenser lens in accordance with the movement (shifting) of the projection lens (for example, see Patent Document 2).
Patent Document 1: Japanese Laid-Open Patent Publication No. 2001-42256 (Pages 4-5, FIG. 3).
Patent Document 2: Japanese Laid-Open Patent Publication No. 2003-75768 (Pages 3-4, FIG. 1).